1. Field of the Invention
The present invention relates to a liquid crystal display device with a touch panel.
2. Description of the Related Art
Touch panels arranged to be overlaid on a display screen of an information communication terminal such as a computer have been widely used as input devices. Liquid crystal display devices, which are generally in widespread use as display devices, are devices that display an image by changing the orientation of a liquid crystal composition confined between two substrates, a thin film transistor substrate (hereinafter referred to as a “TFT substrate”) and a color filter substrate, through a change in an electric field to thereby control the degree of transmission of light transmitting through the liquid crystal composition. In the liquid crystal display devices, the IPS (In-Plane Switching) system in which both pixel electrodes and a common electrode are arranged on the TFT substrate side realizes wide viewing-angle display by forming a so-called lateral electric field.
The touch panel is an input device that recognizes coordinates on the panel touched using a user's finger or the like and causes a processing device to perform processing. For the touch panel, a resistive film system that detects a change in the resistance value of a touched portion, an optical sensor system that detects a change in the light intensity of a portion blocked by a touch, an electrostatic capacitive coupling system that detects a change in capacitance, and the like have been known. The electrostatic capacitive coupling system has been widely used because, for example, it provides high panel transmittance and thus does not reduce display image quality and it provides high durability with no contact with other electrodes.
In recent years, due to the demand for reductions in the size and thickness of information communication terminals, a further reduction in the thickness of a liquid crystal display device with a touch panel has been required. JP 2009-244958 A discloses, in liquid crystal display devices of the IPS system, a liquid crystal display device with a touch panel whose thickness is further reduced by using the common electrode of the liquid crystal display device as the drive electrode of the touch panel.